Robert K. Y. Chan

A light sheet based high throughput 3D-imaging flow cytometer for phytoplankton analysis

This paper reports a light sheet fluorescence imaging flow cytometer for 3D sectioning of phytoplankton. The instrument developed has the inherent advantages of high cell counting throughput and high spatial resolution information derived from flow cytometry and light sheet microscopy. The throughput of the instrument is quantified by the sample volume flow rate of 0.5 μl/min with a spatial resolution as achieved by light sheet microscopy. Preliminary results from 3D morphology of the internal chlorophyll-a structure of two dinoflagellates species show promising application potentials of the method for phytoplankton taxonomy of selected species and species groups.

A fast fluorescence imaging flow cytometer for phytoplankton analysis

We report a fast fluorescence imaging flow cytometer for phytoplankton analysis that can achieve a volume flow rate up to 1ml/min. The instrument shows a high immunity to motion blur in image captured with a lateral resolution of 0.75 ± 0.06 μm for a wide size range ~1 μm to ~200 μm. This is made possible by suppressing the out-of-focus light using thin light sheet illumination and image deconvolution, and by precluding the motion-blur with a unique flow configuration. Preliminary results from untreated coastal water samples show the technique has high potential as a practical field instrument for monitoring phytoplankton abundance and species composition.

Fourier transform ultraviolet-visible spectrometer based on a beam-folding technique

A beam-folding technique in optical interferometry, where the number of beam folds used can be very large, is reported. This technique can be used as a low-cost position-tracking method in a Fourier transform spectrometer (FTS) to cover the broad spectral range from UV to IR. The main advantage gained is the simple position-tracking algorithm used in sampling the interferogram. We have developed a UV-visible FTS, whose wavelength coverage is limited only by the optical elements (350 nm(-1) microm with off-the-shelf components). Preliminary results show that it can achieve a resolution of approximately 4 cm(-1) even with a ball-bearing translation stage.

Toward a UV–visible–near-infrared hyperspectral imaging platform for fast multiplex reflection spectroscopy

A reflection hyperspectral imaging system covering a 350-1000nm spectral range is realized by a UV-visible-near-IR Fourier transform imaging spectrometer. The system has a simple design and good spectral and spatial resolving performance. Accurate and fast microspectroscopic measurement results on novel colloidal crystal beads demonstrate the system has practical potential for high-throughput molecular multiplex assays.

Near UV-near IR Fourier transform spectrometer using the beam-folding position-tracking method based on retroreflectors

A near UV-near IR Fourier transform spectrometer based on a beam-folding position-tracking method realized by using retroreflectors is reported. The use of retroreflectors maintains all beams in the beam-fold arrangement in parallel with the incident beams. The beam-folding interferometer used for position tracking is arranged to have optical path symmetry with the measurement interferometer in the zero path difference position of the measurement interferometer, and the vertex of the movable retroreflector in the measurement interferometer is arranged very close to the midpoint of the vertices of two movable retroreflectors in the position-tracking interferometer. These measures keep the equivalent optical axis of the position-tracking interferometer well in line with that of the measurement interferometer even with translational misalignments. Therefore, the change in the optical path difference of the position-tracking interferometer is always synchronous to that of the measurement interferometer during the scanning process. That is, the position-tracking error can be suppressed to very small values during a scan. We have demonstrated a UV-near IR Fourier transform spectrometer with a standard quality ball-bearing translation stage achieving a resolution close to the theoretical resolution of approximately 0.28 cm(-1) at the He-Ne laser wavelength when the scan distance reaches the travel distance of over 2 cm. This was achieved without the need for elaborate optics, sophisticated detecting electronics, and high-precision servomotion control.

Real-time size distribution, concentration, and biomass measurement of marine phytoplankton with a novel dual-beam laser fluorescence Doppler cytometer

A novel cytometer is reported for measuring particle-size distribution, concentration, and biomass of marine phytoplankton containing chlorophyll a. The system utilizes optical fibers to carry light to and from a flow tube for measuring phytoplankton taken directly from the ocean. A unique feature of this system is in the simple optical detection scheme for which sample handling and preparation are not required. This simplicity makes the system especially suitable for field measurements. The system utilizes sophisticated digital signal processors to handle and reduce the large amount of data gathered. The signal-processing algorithms are vigorously streamlined to process the signals in real time, thus computing size and flow velocity information instead of logging the raw data. The high efficiency of the signal processors gives the system a performance throughput of ~250 particles/s. The system was tested both in the laboratory and in the field, yielding good discrimination of size distribution and sensitivity of concentration.

Tests of a practical visible-NIR imaging Fourier transform spectrometer for biological and chemical fluorescence emission measurements

An imaging Fourier transform spectrometer (IFTS) designed for fluorescence emission measurements is reported. The spectral range extension from NIR to visible of the system is realized by using a simple and low-cost optical beam-folding position-tracking technique. Spectral resolution as high as 9.78cm(-1)(0.4nm at 632.8nm) and maximum image resolution up to 300x300 pixels are proved by the system tests on its optical performances. Imaging fluorescence spectra acquisition of quantum dot clusters and single 200nm diameter fluorescent beads have demonstrated the systems potential for high throughput imaging spectroscopic measurements of fluorescent biological and chemical samples.

Underwater cytometer for in situ measurement of marine phytoplankton by a technique combining laser-induced fluorescence and laser Doppler velocimetry

We present a new type of flow cytometer that can operate underwater for a long time, as long as days, for measuring the size distribution, concentration, and biomass of marine phytoplankton. The major improvement of the instrument over existing techniques is the elimination of sample preparation, which is achieved with a laser Doppler crossed-beam arrangement for both defining a measurement volume and measuring the speed of the particle traversing it. By simultaneously sampling the laser-induced fluorescence signal and the Doppler signals, the technique can discriminate sizes of phytoplankton.

A simple thermal phase stabilizer for real-time optical fibre holographic interferometry

An optical fibre interferometer can be made to phase-stabilize by simply attaching a short length of one arm of the interferometer to a straight copper track and heating the track with an electric current. This feedback thermal stabilization scheme works well even for relatively short fibre lengths and there is no need to treat or unjacket the fibre. A fibre-optic Michelson interferometer stabilized by this method successfully provided object and reference beams for real-time holographic interferometric measurements of the distortion of heated test objects.

Single chip optical fibre interferometer thermal phase-quadrature controller

A simple method of quadrature control for an interferometer is described in which a thermal fibre modulator is provided by a fibre coated with a metal jacket which can be vacuum evaporated or simply painted on, either to the bare fibre or to the jacket. The electronic feedback control is provided by a single power amplifier chip.